The invention relates to a method for determining wear of a force-loaded linkage of an earth-working device and an earth-working device configured for carrying out the method.
Earth-working devices, for example (horizontal) drilling apparatuses and apparatuses for rehabilitating already existing channels in the ground (bores, old pipes), for example expansion devices and pipe pulling devices, typically include a drive apparatus and a linkage, to which the corresponding tool (e.g., the drill head, expansion head or pipe pulling adapter) is attached, connected to the drive apparatus. The drive forces from the drive apparatus are transferred by the linkage to the tool, whereby the tool is advanced in the ground. Pressing forces are typically applied to the tool (the drill head) for a drilling operation of the earth-working device, so that the tool is pushed through the ground. Conversely, pulling forces are typically applied when widening existing bores, bursting existing old pipes and pulling new pipes into existing bores or old pipes. If only pulling forces need to be transmitted, i.e., in an earth-working device which is only used for widening, then cables or chains can also be used as pulling means instead of a linkage. The linkage of an earth-working device consists generally of a plurality of interconnected rod sections which are sequentially connected with each other (in a pushing operation) commensurate with the advance of the tool in the ground or detached from each other (in a pulling operation). The rod sections can be connected, for example, via threaded connections or plug-in couplings. When transmitting the drive forces to the tool with a linkage, only linear drives are employed, which transfer the drive forces and/or drive movements stepwise to the linkage, i.e., with a load stroke, where the linkage is connected with the linear drive, and an idle stroke, wherein the connection between the linear drive and the linkage is released. All conventional linear drives for earth-working devices operate with hydraulic cylinders as drive source, because these are able to produce the large forces while having comparatively compact dimensions. However, linear drives with rack and pinion drives are also known.
If only pulling forces are to be transmitted (in particular, if additional use as drilling device is not contemplated), then pull cables or chains can also be used for transmitting the drive forces to the tool. The pull cables or chains can either also cooperate with the linear drive, which then must have corresponding clamping elements for affixing the pull cable or chain, or may be used with (hydraulic) winches.
A problem has surfaced during use of the aforedescribed earth-working devices in that the expected service life of fundamentally all components of this device, however in particular of the force transmitting element (i.e., the linkage, the pull cable or the chain), is difficult to estimate. This is particularly due to the fact that the service life of the components depends on how the load is applied, in addition to the geometric dimensions and the employed material. In particular, the magnitude of the applied forces and the fraction of dynamic loads to the total load affect the service life of the components. The fraction and the magnitude of the dynamic, i.e., non-static loads (i.e., loads with a constant force from a constant direction) in earth-working devices depend in turn significantly on the external circumstances (e.g., the conditions of the ground) and the employed drive apparatus. In addition, the time at which a rod section is inserted in the strand of a linkage, has a significant effect on the loads to which this rod section is subjected during the performed earthwork, and hence on the service life of this rod section.
The loads on the linkage cause material fatigue which increases with the fraction and the magnitude of the dynamic loads on the total loads. Material fatigue can cause cracks at geometric weak points (e.g., notches or other transitions in the cross-section) and material-related flaws (e.g., material inclusions), which propagate with progressing rocker number of the dynamic loads and finally result in failure of the linkage due to breakage or tearing. This can be associated with a significant safety risk for the operating personnel of the earth-working device, if a rod section which is still in the working draft fails, or can lead to additional work, in particular when the cracked rod section can only be retrieved by digging.
A number of computation methods have been developed to calculate an expected service life of a dynamically loaded component, wherein particularly the magnitude of the loads and the frequency of the occurrence of these loads is evaluated—in addition to the geometric dimensions and the employed material of the respective component—and used for estimating the expected service life.
Starting from the current state-of-the-art, it was an object of the invention to increase the operating safety of an earth-working device of this type.